Control system



y 1935'. v.0. ANDREW 2,000,685

CONTROL SYSTEM Filed June 2'7,v 1931 4 Sheets-Sheet 1 C'onfr-o/ Oscl /afor Canfrv/ Osc/l/afor WITNE5$E$ V INVENTOR BY J ' AT'TO EY May 1935- v. J. ANDREW 7 2000,685-

CONTROL SYSTEM I Filed June 27, 1931 4 Sheets-Sheet 2 Take 1.

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7Zbe 1 ATTORN Y May 7, 1935.

V v. J; ANDREW CONTROL SYSTEM- Filed June 27, 1931 4 Sh eets-Sheet 3 NN 0 km N U D Y m w ol R Q 7 1* v a PIJQ Q RKk RU v 'w v d P1 9 yqquzyo .p/Jg

' INVENTOR WC/orfflndrem W ATTORNEY May 7,1935. v. J. ANDREW 2,000,685

CONTROL SYSTEM Filed June 27, 1031 4 Sheets-Sheet 4 v fTgr 7.

I 33 35 1|||l|m|||r WWW/v WITNESSES; INVENTOR I I w cforfflflorew ATTORN EY Patented May 7, 1935 UNITED, STATES I oon'mor. srs'rim I r v vVictor J. Andrew, Wooster, Ohio, Westinghouse Electric & ManufacturingjCom- 'pany, a corporation ,of Pennsylvania] Application June 27, 1931', Serial No. 547,305 4 Claims. (Cl. asp-3'6) '1 My invention relates to oscillation generators, more particularly to means 'for controlling the frequency and stabilizing the operation thereof.

It is one object ofrmy invention to provide 5 means for controlling the'frequency of an oscillater which means shall exert its controlling influence over a greater shift in the frequency or the oscillator than-heretofore. 7

Another object of my invention is to provide means whereby the frequency of an oscillator may-be controlled only by alternate harmonic frequencies 01' its fundamental.

Another object or my invention resides in a simple and convenient means whereby the above objects of my invention may be realized. Additional objects or my invention will be disclosed in the following description of the same, taken in conjunction with the accompanying drawings wherein:

Figs. 1,2, '7 and 8 are schematic diagrams representingembodiments and modifications or my invention. a 1 p Figs. 3, to 6, inclusive, are curves illustrating the manner of operation of my invention'under various conditions, as will be more clearly pointed out in the following description. g

It is common practice to utilize as a source of frequencies containing a plurality of harmonics, various types of oscillation generators. In choosing a generator for this purpose, it is .desirable to pi ck one of that type which will generate a wave approaching that of a square or substantially square top wave. It has been found that such a wave contains a practically unbroken and unlimited series of harmonics. f V

An oscillation generator having this charac teristic to a marked degree is one commonly termeda multivibrator. In Figs. 1 and 2, of

the accompanying drawings, I have illustrated oscillation generators of the multivibrator type. 'A generator of this type comprises a pairof thermionic devices I and 3 coupled together bycapacitles and resistances and so arranged as toproduce alternate discharges spontaneously. In Figs. 1 and 2, wherein I have disclosed an oscillation generatorof this type, it will be noted that the circuits associated with the thermionic devices aresymmetrically arranged with regard to each other; The grid circuit of each tube comprises aresistor 5 or l connected between the filament and grid of its respective tube. The plate circuits of the tubes also comprise resistors! and H, both connected between the plates 01' their respective tubes and the positive terminal of a common plate potential supply unit llLthrough a Ordinarily, it

coil 15, the negative terminal of the plate supply unit being connected'to the common grounded filament connection. Between the plate of each tube and the grid of'the other, there is connected .a variable condenser 4' or 6, respectively, by means of which changes maybe made in the adjustment of the circuits. p f *The coupling system shown by coils l5 and I!) might equally well'be any other coupling device and. might vbe connected in any manner .which .would introduce the coupling frequency to both tubes. symmetrically; One other manner consists in inserting sucha system of coupling coils. between the grid resistors and the filament. V would appear-in apsystem embodying symmetrically arranged circuits as shown, that the circuits would 'be balanced and, therefore, a stable condition would exist therein. While this condition should exist theoretically, such a condition is not maintained by reason of the fact that various unbalancing influences prevail which cause an arrangement of the type disclosed. to be amost unstable one. Slight differences in the corresponding elements'oi' the system, theyeflect of sound waves impinging on the 5 tubes; etc., all tend to upset the balance 01' the system. J

.Assume that some such disturbing influence causes a slight increasein' the' plate current of tube I. This will produce an increase in the potential drop across-the resistor 8 in the plate circuit of that tube which will [resultin a reduction of' the platevoltage on the anode oi the tube l. This change of potential acting through the variable condenser 8 connecting the plate of the tube! with the gridjof the other tube 3, will reduce the voltage on' the grid of the second tube 3. This decrease or potential willjnecessarily result in a corresponding decrease in the plate. current of 'this'second tube, the drop in plate current beingmany times greater than the slight increase 01' current in .the plate circuit of the first tube. The reduced current will decrease the potential drop across the resistor II in the plate circuit of the second tube 3, thereby increasing the potential on the plate of said tube. This increase in plate, potential on said'tubeii acting through the variable condenser 4 located between the plate of the'tube 3 and the grid of the tube 1| will serve to further increase the potential on the grid of the first tube. Accordingly, this increase will still'further increase the plate current oi the first tube I with a further decrease in the grid potential of the secondtube 3, etc. The above cyclic'phenomenon constitutes a transient charges on the condensers, at this point, they. will accordingly discharge through resistors ,5.

and 1 or 9 and II, respectively. During the discharge period, the potential on the grid ofthe second tube 3 will build up to a point where plate current in that tube will again begin 'to flow,

' tube.' Curve 23 represents the current flow in a at which time another transient conditionf'will be set up, but in a direction which will be opposite to that transient described above.. These alternate discharges between the tubes of the system will continue so long as energy is supplied from the source of plate potential supply and the A battery supply. The frequency .of these discharges may be controlled by varying the values of the condensers and/or the resistors.

In. utilizing any oscillation generator as a source of high frequencies it is .very desirable, where accuracy is necessary, to controlthe fundamental frequency of the generator to prevent it from shifting in frequency from that of its designed value toa value closely adjacent thereto. To obtain this result, it is common practice to employ a control frequency wavewhich is impressedupon the clrcuitof the oscillation'generator, the frequency of the control wave bearing an harmonic relationshipto the fundamental frequency of the generator;

In the methods and means commonly resorted to, according to the prior art, if the frequency of the generator should, for any reason, shift nearly to an adjacent sub-harmonic ofthe control'frequency, the, tendency would exist, whereby the control frequency would now function to alter and maintain the fundamental frequency of generator at the adjacent sub-harmonic. Thisyof course, is not the result desired, and by my .invention, I have provided means whereby. the frequency of the generator may shift between wider limits without being pulled out of step with its original fundamental; frequency as described above. 1 More specifically, according to my invention, the frequency of the generator will have to shift twice as far as heretofore, before the control frequency will tend to pull it out of its original value.. I a

Referring more particularly .to the drawings, I have disclosed two modifications whereby the above results may be, obtained. In the modifications, I have illustrated the oscillation generator in, combination with a source of control frequencies, the particular results obtained arising out of the manner in whichI have coupled the control frequency source .to the oscillation generator. I

According to the modification disclosed in Fig. 1, I'connect the positive terminal of the plate supply source to the mid-point l1, of the coil l5 which is connected in the plate circuit. of the tubes. The outputcircuit I9 of the control frequency source 2| is coupled to this coil 15 as clearly illustrated in' the circuit disclosed and described by .me. The control-frequency potential induced in the coil of the oscillation generator will, by reasonof thedescribed connection, be impressed upon the anodes of the thermi nic (18* ditions of wave form. The upper half of the flgurerepresents the transient effects existing in one tubeand the lower half representing the operation of the second tube.

In the figure, three curves are shown for each multivibrator circuit under substantially ideal conditions, curve 25 the control frequency impressed upon the multivibrator circuit and curve 21, the resultant characteristics of the current in the multivibrator circuit as altered by the impressed control frequency. The brokenline 29 indicates the cut-off point on the tubes in the multivibrator circuit. The cut-off point is that value of grid potential which reduces the plate current tozero. When the grid potential of one tube passes above the cut-off point, a discharge takes place through the two tubes of the circuit. Thecircuitzdisclosed in Fig. 1 is designed to provide control of the fundamental frequency of the oscillator at odd sub-harmonics only of the control frequency' This result is obtained by reason of the particular coupling connection to the control frequency source. As noted above, the

control frequency potentials will be impressed upon the tubes of the oscillator equally but in opposite phase relationship. In Fig. 3, curves 25 represent control frequency as impressed upon the tubes of the oscillator and in this particular case, the control frequency bears an odd harmonic relationship to the fundamental frequency of the oscillator and is shown impressed equally but in opposite phase relationship upon the tubes of the oscillator; Outside of the fact that the cut-off point is. reached sooner than when the control frequency is not applied, no change'occurs in the frequency relationship existing between the fundamental of the oscillator and that of the control frequency, and the oscillator will, therefore, continue to oscillate at its designed frequency.

, Should the fundamental frequency of the vi.- brator or oscillator tend to shift for any reason to a value which bears an even sub-harmonic relationship to the impressed control frequency, an unstablecondition will develop and the fundamental frequency of the oscillator will be brought bacl; to its odd-sub-harmonic relationship. This unstable condition and the manner in which the by means of a crystal or tuning fork control. It

will be seen that the even-sub-harmonic relationship cannot exist for any appreciable length of time, for within each half cycle, the phase of the oscillator will be shifted enough to make the length of the half cycle equivalent to an adjacent odd-sub-harmonic of the control frequency.

It will be apparent, therefore, in a circuit as disclosed'in Fig. 1, that the frequency of the oscil- Lil which, accordingly, 1 rapidly discharges 'its'ab-' lator will be controlled at odd-sub-harm'onic' frequencies only'of'the control frequency. The control frequency, consequently, will function'as 'a control'throughout a frequency range which will be substantially twice'asgreat as in similar circuits of the'prior art known by me; In' other words, the natural frequency of the oscillator will have to shift twice as far as previously necessary, before it will be beyond the" power of the control frequency to bring it back to its original frequency. r I I 1 In Fig. 2, the coupling of the controlfrequency source to that of the oscillator is'of such'a character that the frequency of the oscillator can be controlled at even-sub-harmomcs only of the control frequency. Theoperation of this circuit is clearly illustrated by means of the curves of Figs. and 6 bearing reference numerals similar to those applied to the curvesof Figs. 3 and 4.

Fig. 5 represents a condition wherein the frequency of the oscillator bears an even sub-harmonic relationship to thatof' the control frequency in a circuit such as shown in Fig. 2." As in the circuit of Fig. 1 under the condition exemplified in Fig; 3, the only effect of the control frequency upon the fundamental frequency of the oscillator is to shift the time at which cut-off occurs. Outside of that, no material changes are produced. The frequency of the oscillator is maintained, and should it for any reason tend to shift from its designed frequency, the control frequency will function to bring it back to its normal frequency. The manner in which this controlling function operates is illustrated by means of the curves of Fig. 6 where an extreme case is taken as an example. The condition illustrated in Fig. 6 exists when the frequency of the oscillator has, for some uncontrollable reason, shiftedv to an adjacent sub-harmonic which bears an odd sub-harmonic relationship to the control frequency instead of an even sub-harmonic. By reason of the particular coupling employed in the system of Fig. 2, the control frequency will be applied equally and in phase to both tubes of the oscillator, as clearly illustrated in both Figs. 5 and 6.

The frequency of the oscillator as represented by curve 23 of Fig. 6 will be changed to a. frequency corresponding to curve 21. When this new frequency is compared to that of the control frequency, it will be found that it bears an even sub-harmonic relationship to that of the control frequency. In order, therefore, for the fundamental frequency of the oscillator to be pulled out of its designed frequency, it will have to shift somewhere in the neighborhood of the next even sub-harmonic which, of course, means that the shift must be approximately twice as much as in former similar systems wherein the frequency of the oscillator would be pulled into its closest sub-harmonic frequency whether that frequency be an even or odd sub-harmonic.

In Figs. 7 and 8, I have illustrated my invention as applied to oscillators of the neon tube relaxation type. As oscillator of this type comprises one or more neon tubes shunted by a capacity parallel with a source of potential. The operation of an oscillator of this .type may theoretically be explained as follows. The source of potential sends a charging current through a limiting resistor, to both the neon tube and the capacity shunting it. When the potential built up across the tube reaches the break-down value of the tube, the tube breaks down providing a conductive discharge path for the capacity sorbedenergy through {the tube. The potential across the tube thereby is reduced sufliciently to bring it back to its initial non-operating condition, ready for I another charge whereupon-the cycle isautomatically repeated; The particular oscillator of..-:this t disclosed by me "comprises a pair-ofsineon tubes-3l-connested in series across a source of potential '33 anda current limiting resistor 35:; Capacities 3], preferably similar in characteristics, areshunt'ed across each .tube. respectively The source of'potential 33- should beof such value'as to produce" break-fdown in the'two tubesinseriesfi Whenlthe breakdown potential. isireachede the capacities 31, which have been charged to the break-down potential, will. discharge :through their respective tubes in the manner described above. odic charge and discharge'of the c'ondenserswill produce an oscillatory current of a. definite'frequency, depending upon the valueof the constants of the system. 4

. In the particular embodiment disclosediniFigfl,

a coil 39 which is substantially'evenly divided; be.- tween the twoz-condenser'circuits";is inductivelycoupled to the coil 4|, which coil comprises the output of a control frequency source. The control frequency potential will, therefore, affect each tube simultaneously and similarly and, as in the' case of the multivibrator circuit of Fig. 2, wherein the both tubes were affected in the same manner and simultaneously so the control frequency will function to control the fundamental frequency of the oscillator at even sub-harmonics only of the control frequency.

In the modification disclosed in Fig. 8, the coil 39 is inserted in that portion of the system which is common to the both condenser circuits, and is coupled to the coil 4| whereby the control frecontrol frequency will function to control the fundamental of the oscillator at odd sub-harmonies only of the control frequency.

Throughout the specification, I have used the term frequency in a generic manner as applied I to current or potential at that frequency.

Since, according to my invention, the frequency of the generator may be controlled, at either the odd or the even sub-harmonics only, according to the circuit used, I have referred to the even or odd.

harmonics as constituting alternate harmonics and have so expressed them in the claims.

While I have disclosed my invention in great detail, it will be apparent thatvarious changes might be made within the contemplated scope of my invention, and I, therefore, do not desire to be limited to the'speciflc details described, except insofar'as is necessitated by the prior art and by the appended claims.

I claim as my invention;

1. In combination a control frequency source, means for producing an oscillatory condition comprising an oscillator of the multi-vibrator type including a pair of discharge devices, the frequency of said oscillatory condition bearing a definite sub-harmonic relationship to that of the control frequency, and means for impressing upon each of said discharge devices an alternating potential derived from said control source, said potentials being 180 degrees out of phase with each other. I Y

2. In combination, a pair of electron discharge devices, each having an anode, a grid and a cathode, inductance connecting said .anodes, a

source of energy connected between said cathodes and substantially the mid-point of said inductance, a capacitor connected to each of said anodes and a separate impedance connected between each of said capacitors and said cathodes, a connection from the grid .of each of said discharge devices to the junction of that capacitor and its associated impedance which is connected to the anode'of-the other discharge device, and means :cathode, inductance connecting said anodes, a

source of direct current energy connected between said cathodes and substantially the midpoint of said inductance, a'capacitor connected to each of said anodes and. a separate impedance connected between each of said capacitors and said cathodes, a connection from the grid of each ofsaid discharge devices to the junction of that capacitor and its associated impedance which is connected to the anode of the other discharge device, and means for impressing an alternating electromotive force across the inductance connecting said anodes.

4. In combination, a pair of electron discharge devices, each having an anode, a grid and a cathode, inductance connecting said anodes through resistors individual to said anodes, a source of energy connected between said cathodes and substantially the mid-point .of said inductance, a capacitor connected to each of said anodes and a separate impedance connected between each of said capacitors and said cathodes, a conanection from the grid of each of said discharge devices to the junction of that capacitor and its associated impedance'which is connected to the anode of the other discharge device, and means for impressing an alternating electromotive force across the inductance connecting said anodes.

VICTOR J ANDREW. 

